An electronic apparatus including a handheld terminal such as a cellular phone and a PDA, and a notebook-sized personal computer is supplied with electrical power by a power source such as a battery in order to ensure the portability of the electronic apparatus. Although a rechargeable battery is in widespread use as the power source, a fuel cell such as a polymer electrolyte fuel cell will be substituted therefor in near future.
The current trend is that the electronic apparatus is provided with a variety of extended functions, resulting in increase in required electrical power. Meanwhile, the electronic apparatus must consume reduced electrical power to ensure operating time of the electronic apparatus. These two conflicting issues of the electronic apparatus, i.e., improved electronic apparatus functions and reduced power consumption, must be smoothed out.
To achieve less power consumption in the electronic apparatus, a power source system having proper control of the electrical power to be supplied is disclosed by cited Reference No. 1 or published Japanese Patent Application Laid-Open No. 2004-88853.
FIG. 16 is a block diagram illustrating a power source system disclosed in cited Reference No. 1.
The power source system 100, which is operable to supply a load circuit 106 with the electrical power, includes elements as discussed below. A power-supplying source 101 such as a rechargeable battery is an electrical power supplier. The load circuit 106 includes all electronic circuits that must be supplied with the electrical power, such as various electronic components, IC's, and a display panel, each of which actuates the electronic apparatus. The power-supplying source 101 includes a power source terminal 102 connected to both a switching regulator 103 and a series regulator 104. A control unit 105 is operable to select either the switching regular 103 or the series regulator 104 to use the selected regulator. The load circuit 106 is supplied with the electrical power through the output from the selected regulator.
Although the power-supplying source 101 has a certain output voltage, the load circuit 106 has an operating voltage often varying in dependence upon the circuit structure and electronic components, and the output voltage of the power-supplying source 101 must be lowered to supply the load circuit with the electrical power. To this end, the switching regulator 103 and series regulator 104 are provided for lowering the voltage.
As illustrated in FIG. 17, the switching regulator 103 differs in efficiency characteristics from the series regulator 104 relative to consumption current. FIG. 17 is an illustration showing the efficiency characteristics of each of the switching regulator and the series regulator.
Referring to FIG. 17, according to the efficiency characteristics of the switching regulator 103, the efficiency is shown on the increase with an increase in consumption current in the range of a smaller consumption current, but is shown saturated when the consumption current is equal to or greater than a predetermined value. With continued reference to FIG. 17, according to the efficiency characteristics of the series regulator 104, the efficiency is shown remaining unchanged relative to a definite value regardless of variations in consumption current. In consideration of such efficiency characteristics, the series regulator 104 is selected when a smaller consumption current flows in the load circuit 106, but the switching regulator 103 is selected for a certain or greater consumption current. Such a switchover supplies the load circuit 106 with the electrical power in response to variations in consumption current.
However, increased consumption current in the load circuit 106 reduces the output voltage of the power source terminal 102. To be specific, the increased consumption current in the load circuit 106 results in a drop in voltage, thereby reducing the output voltage of the power source terminal 102. The reduced output voltage brings about a problem of malfunction of the load circuit 106. In particular, when the power-supplying source 101 is a fuel cell, a much greater reduction in voltage occurs.
Alternatively, assume that the power-supplying source 101 includes a margin for the reduction in output voltage. However, as a result of the alternative, a higher voltage is objectionably supplied to the load circuit 106 although the load circuit 106 requires a smaller consumption current, with a consequential increase in unwanted power consumption. In addition, a difference between input and output voltages of each of the switching regulator 103 and the series regulator 104 is increased, thereby increasing a voltage amount required to lower the voltage in each of the switching regulator 103 and the series regulator 104. This causes another problem of increased loss of power consumption in each of the switching regulator 103 and the series regulator 104 as well as that in the load circuit 106.
In conclusion, the prior art power source system has problems as discussed below.
One of the problems is that the inability of the proper supply of the electrical power to the load circuit 106 results in increased power consumption. The increased, unwanted power consumption brings about another problem of reduced operating time of an electronic apparatus.
A further problem is that the power reduction-caused malfunction of the load circuit results in reduced reliability of the electronic apparatus in terms of electronic apparatus activities.